Science File

Scientists Vindicated: Bees Can Fly; Here's How

Scientists have long been derided because of mathematical calculations made in 1934 by French entomologist August Magnan proving that, despite visible evidence to the contrary, the flight of bees was "impossible."

But now bioengineer Michael H. Dickinson of Caltech and his colleagues have shown conclusively how the hefty insects manage their aeronautical excursions.

Dickinson's team used a combination of high-speed digital photography and a giant robotic mock-up of a bee wing to demonstrate the unusual mechanics behind bee flight.

The secret, they reported this week in the Proceedings of the National Academy of Sciences, is a combination of short wing strokes, rapid rotation of the wing as it changes direction, and very fast flapping.

Virtually all insects flap their wings through a wide arc, about 165 degrees. Frequency generally varies with size: The larger the insect, the slower the wings beat. Mosquitoes, for example, beat their wings about 400 times per second, fruit flies about 200. Birds beat their wings much more slowly -- about 50 times per second for hummingbirds.

But bees, which are 80 times as large as fruit flies, flap their wings 230 times per second through an arc of about 90 degrees. And although most insects produce the majority of lift about halfway through the stroke, when the wing is moving fastest, bees get an equally large contribution at the beginning and end of the stroke from the rotation of the wing.

Bees, moreover, do not vary their beating rate when carrying a load. Instead, when burdened with pollen, they increase the arc of flapping, Dickinson found.

"The wings have to operate fast and at a constant frequency or the muscle doesn't generate enough power," he said.

It is possible that the muscles evolved in this fashion specifically to support bee flight, he said, but it is equally likely that "bee ancestors inherited this kind of muscle, and now present-day bees must live with it."